1. Field of Invention
This invention relates to an apparatus for circulating and distributing an electrolyte through a multisection battery.
2. Description of the Prior Art
Battery systems are well known which utilize a circulating electrolyte such as a metallic halogen; zinc-chloride, for example. Such a battery system is illustrated in U.S. Pat. No. 3,713,888 issued to the same assignee as the present invention. The electrolyte is generally pumped through the system and to electrodes at which an ionic exchange occurs and a potential difference is created across the electrodes. This source of energy can be used to electrically power motor vehicles or serve as a standby power reserve and in many other situations where electrical energy is needed for a long-term use.
There are three major difficulties associated with circulating electrolyte around an electrochemical battery. First, the electrolyte is usually highly corrosive, for example, in the zinc-chloride system the electrolyte is zinc chloride and is commonly circulated containing free and dissolved chlorine. Second, in multi-section batteries containing more than one cell, conductivity of the electrolyte is usually high enough so that electrical leakage from one cell to another occurs producing electric shorting circuits flowing in the electrolyte which substantially increase intercell power losses. In a zinc-chlorine battery operating at 250 volts, the single circulation path 1/2 inch in diameter and 12 inches long bridging the entire battery cell structure has been observed to result in a power loss of as much as 300 watts due to electrical leakage along the circulation path. Because of the leakage problem from one cell to another, the design of circulation paths in electrochemical batteries has become a critical factor. Third, the circulation requirement for the electrolyte in the battery is usually for relatively high flow rates at relatively low pressure drops. This requirement is conventionally met by relatively cumbersome pumping devices. In the zinc-chlorine system, chlorine is commonly delivered to the battery cells in solution in the zinc chloride electrolyte requiring that the battery cells be fed with electrolyte in parallel rather than in series. A typical flow rate of 40 gallons per minute at a pressure drop of 2 pounds per square inch is used.
In conventional battery systems, particularly those designed for mobile use where space and weight are at a premium, the combination of the above difficulties leads to a number of unsatisfactory compromises between weight, volume, power efficiency and reliability. For example, the corrosive nature of the electrolyte requires that the use of mechanical seals and magnetic couplings be held to a minimum. The high-flow, low-pressure drop requirement leads to low speed, high torque electrolyte circulating devices which tend to be heavy, are cumbersome and rely on magnetic couplings and motors for their operation. The electrical leakage problem leads to subdividing the circulation system into a number of electrically isolated cells with the provision of a sequenced valve arrangement so that electrolyte only flows to one of the cells at a time, each cell being supplied with electrolyte in turn by sequenced opening of the valve. Such a cumbersome system is shown in British Pat. No. 1,249,308. Furthermore, even compromising these difficulties, reduction in weight and size of the circulating system is only possible by sacrificing power efficiency.